This invention relates to an automatic sewing machine and more particularly, to an automatic sewing machine for continuougly sewing a workpiece having a plurality of contiguous edges connected together in angular relationship to each other.
In continuously sewing a workpiece having a plurality of contiguous edges connected together in angular relationship to each other, such as a pair of trousers, after a first edge of the workpiece has been sewn, in order to sew a second edge of the workpiece it is necessary to turn the workpiece about the position of the sewing needle so as to align the second edge with the advancing or feed direction of the work.
One of the conventional methods for turning the workpiece in the manner mentioned hereinabove has been illustrated in U.S. Pat. No. 3,425,369, for example. According to this prior art turning method, after a first edge of the workpiece has been sewn, a vertically movable turning member is lowered down onto a portion of the workpiece which hangs from the tabe to hold the workpiece portion against the surface of the table, the turning member is turned with the workpiece portion held against the table surface, and the workpiece is turned about the position of the sewing needle on the table until a second edge of the workpiece contiguous to the first edge thereof is detected by a detection means which is adapted to detect whether or not the second edge is aligned with the sewing or work advancing direction. However, in the conventional workpiece turning method, since the turning member is designed to turn the workpiece by a predetermined angle while holding the workpiece in a predetermined position or constant distance from each of the workpiece edges, there is the disadvantage that the turning member can not positively engage the workpiece portion inwardly of a second edge of the workpiece when the member turns to the workpiece after a first edge of the workpiece has been sewn. That is, generally, since a plurality of contiguous edges of a workpiece are not in constant angular relationships, or have varying angular relationships to each other, the turning member tends to engage the workpiece in a position excessively inwardly of a particular edge of the workpiece and in a position excessively outwardly of another edge of the same workpiece. That is, it can not be assured that the turning member always engages the workpiece in a predetermined constant distance from all the edges of the workpiece. When the turning member engages the workpiece at a position excessively inwardly of an edge of the workpiece, the edge is caused to crease and thus, even if the creased edge can be aligned with the work sewing or feed direction, a satisfactory or proper sewing operation can not be performed at such an edge. On the other hand, when the turning member engages the workpiece at a position excessively outwardly of a edge of the workpiece with the contact face of the turning member maintained nonparallel to the surface of the table, the turning member can not positively hold the workpiece edge and tends to disengage from the workpiece while the workpiece is being turned, whereby the workpiece edge can not be brought to the alignment with the work sewing or feed direction. In order to eliminate such disadvantages, it has been proposed to construct the turning member so as to have a sufficiently large size and cause its contact face to maintain a parallel relationship to the surface of the table. But even with such a turning member, there are still the disadvantages that a crease or creases develop in the edge of the workpiece and the edge can not be positively held down.
Furthermore, in the prior art method mentioned hereinabove, in the waiting position of the turning member, if the turning member is positioned in a position insufficiently spaced from the table surface during a sewing cycle, the turning member is contacted by a crease or creases developed in the workpiece edge to impede the sewing operation. And when the turning member is again moved to the workpiece holding-down position at a location insufficiently spaced from the table surface for the next workpiece turning operation after one workpiece turning operation, the turning member comes into contact with the crease or creases in the workpiece edge to the degree that the sewing result will be unsatisfactory. For this reason, it is necessary that the turning member has to be positioned at an otherwise unnecessarily great distance from the table surface. This appreciably prolongs the time required for the workpiece holding-down operation by the turning member and renders the construction of the turning member complicated.